1. Field of Invention
The present invention pertains to a container for carbonated beverages and more particularly, it pertains to a container having applied to the internal beverage contacting wall surface an inert, water insoluble polymeric layer which suppresses carbonation loss from beverages packaged therein.
2. Prior Art Metal containers used for the packaging of carbonated beverages such as beer and soft drinks have applied to the internal wall surfaces an inert, water resistant or hydrophobic polymeric organic coating which protects the metal surface from corrosive attack by the carbonated beverage packaged therein. It has been observed that upon the filling of these metal containers with the carbonated beverage product and also when the sealed containers are subsequently opened, carbonation is lost relatively rapidly and the beverage may acquire a flat taste. High carbonation loss from the carbonated product of newly opened metal containers as well as from plastic bottles formed from synthetic organic resins such as polyethylene terephthalate is quite typical. The carbonation loss rate may be so great that the liquid actually "gushes" out when the container is opened.
The art has attempted to eliminate the carbonation loss problem by coating the internal surface of the containers with oleic acid, e.g., U.S. Pat. No. 4,069,933, or glycerol, e.g. U.S. Pat. No. 4,091,954. These prior art attempts at reducing carbonation loss have not been entirely successful as the coating material has either imparted an off-flavor and/or odor to the carbonated beverage or the reduction in carbonation loss is inconsistent due to the transient nature of the coating material.
In a study by the present inventors of CO.sub.2 loss occurring when carbonated beverage containers are opened for use, it was found that higher rates of loss occur when the beverage is packaged in metal containers internally coated with inert hydrophobic organic polymeric materials or bottles formed from hydrophobic thermoplastic resins such as polyethylene terephthalate (PET) as compared with glass containers. It was concluded that the greater loss rate was due to the differences in roughness and water repellancy of the hydrophobic polymeric surfaces as compared with glass surfaces.
Glass is an inorganic material which is quite hydrophilic and is a relatively smooth surfaced product. Water wets clean glass surfaces well. Due to their chemical composition, polymeric materials such as the vinyl halide polymers typically used as metal container coatings and the thermoplastic resins used in bottle manufacture, e.g., polyethylene, polyvinyl chloride and PET are quite hydrophobic, with the result that water exhibits poor wettability to those materials. Also relative to glass surfaces, the surface of these polymeric materials is not smooth and has many microscopic imperfections and fissures. Due to the poor water wettability of these polymeric materials, upon filling containers in which the exposed internal wall surfaces are composed of such hydrophilic materials, gas entrapment occurs within the microscopic fissures in the polymeric surface. If the surface is hydrophilic, water flows into the fissures and displaces the trapped gas.
Gas entrapped in the fissures present in the polymeric surfaces serves as a nucleus for bubble formation and growth and subsequent carbonation loss when the beverage container is opened.
Excessive bubble nucleation causes the carbonated beverage to gush out of the container when the container is opened for use which is very undesirable from the consumer standpoint.